Head up displays (HUDs) for automotive vehicles comprise an image source for forming an illuminated pattern to be projected onto the windshield for reflection to the eyes of the vehicle operator. Then the display information is visible to the operator by looking straight ahead, and it is not necessary to look away from the road to read an instrument. A system of mirrors is used to direct the display image from the source to the windshield. The same system of mirrors can capture external light incident on the windshield and illuminate the source. The source typically comprises segments which are selectively illuminated to create the desired pattern, for example, a number. If, however, the non-selected segments are illuminated by incident light, they may appear to be part of the illuminated display. Incident light from bright sunlight as well as overhead street lights can produce such an undesirable effect.
It is known in the case of CRT displays or other conventional displays to use circular polarizers as glare filters. However, in the case of a HUD, polarization of the image already occurs at the windshield reflection and additional polarization of the image can result in reduction of image brightness, even to the point of completely extinguishing the image.